Endotracheal tubes intended for insertion through the mouth, nose or implanted in the neck (oro-naso and tracheostomy tubes) are usually provided with an inflatable cuff for sealing against the tracheal wall. The efficiency of the sealing is determined by the magnitude of the cuff pressure against the tracheal wall since the inflated cuff does not seal off pressures exceeding the pressure of the cuff against the wall. The air pressure in the cuff determines the pressure against the tracheal wall. The pressure of the cuff against the tracheal wall can be controlled and regulated only if the cuff has a sufficiently large diameter to make contact with the tracheal wall without any stretching of the sheet material of the cuff, i.e. the cuff must be lying folded on the tracheal wall. If this demand is met, the pressure in the cuff is identical with its pressure on the wall.
If the pressure of the cuff against the tracheal wall is considerably higher than 30 cm H.sub.2 O, the blood supply to the mucosa is occluded, and this causes damage in the form of superficial or deeper ulcerations after some time. This damage is prevented in that the sealing cuff, lying folded on the wall, is kept inflated from an outer pressure source with a constant, regulated pressure of 20 to 30 cm H.sub.2 O.
The sealing cuff has the additional function of preventing liquid (blood, saliva, vomit) from flowing past the cuff down into the lungs. It has been found that this function is accomplished when the pressure of the sealing cuff against the tracheal wall is at least 20 to 30 cm H.sub.2 O.
Spontaneous changes in the diameter of the trachea, changes in the catheter position and the diffusion of certain anaesthetic gases through the wall of the sealing cuff may cause considerable changes in the pressure in the sealing cuff if the inflation pressure is not controlled and regulated.
During artificial respiration the necessary pressure of the respiration air may often exceed 20 to 30 cm H.sub.2 O, and the pressure in the sealing cuff is then too low to seal off the pressure of the respiration air.